linux-kernel - Re: [PATCH 2/2] rust: alloc: add `Vec::dec

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Message-ID: <Z9gF90wPSZTRQfRR@pollux>
Date: Mon, 17 Mar 2025 12:22:31 +0100
From: Danilo Krummrich <dakr@...nel.org>
To: Tamir Duberstein <tamird@...il.com>
Cc: Andrew Ballance <andrewjballance@...il.com>,
	Alice Ryhl <aliceryhl@...gle.com>, Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Trevor Gross <tmgross@...ch.edu>, rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] rust: alloc: add `Vec::dec_len`

On Sun, Mar 16, 2025 at 07:27:22PM -0400, Tamir Duberstein wrote:
>
> Does this suit?

I think for dec_ref() it is not the safety requrement that justifies the
invariant.

I think it should be something along the lines of:

	// INVARIANT: We drop ownership for all elements within the range
	// `[self.len - count, self.len]`, hence the updated value of `set.len`
	// represents the exact number of elements stored within `self`.

> 
> >         // INVARIANT: By the safety requirements of this method `self.len - count` represents the
> >         // exact number of elements stored within `self`.

Please do not use the email quote mechanism for code snippets, it's confusing
for readers to figure out by whom it has been written.